The present invention relates to a porous structural materials having a solid shape with a curved surface of which the dimensional accuracy is high, and structural materials composed of plural layers and containing one or two metal sheets bonded metallurgically to the surface thereof. This invention also relates to process for forming the porous structural materials highly accurately.
In general, metal sintered body having a flat plate shape has been produced by compacting metal powder as raw material under a high pressure and heating the compacted powder at a high temperature lower than the melting point according to powder metallurgy. In the conventional powder metallurgy, as the powdery raw materials, reduced iron powders made from iron ores and mill scales, electrolytic iron powders, atomizing powder and so forth are used. Produced metal sintered bodies are porous, having voids remaining therein. The voids are very fined and tight. Since the voids present in the metal sintered bodies are tight, the sintered bodies have no vibration- and sound-absorbing properties and also no gas permeability.
A method of molding a metal sintered body having large pores has been proposed in Japanese Patent Publication No. 58-52528. I am one of the inventors of the Japanese Patent Publication No. 58-52528. In this molding method, a porous sintered plate can be produced by pressing metal chips with heating while being electrified. The obtained sintered plate is superior in sound absorption, sound insulation and anti-vibration. The sintered plate is used in a variety of fields, as sound absorbers for concert halls and listening rooms, sound insulating plates for floor and wall boards in houses, and sound-proof and anti-vibration materials for vehicles and ships.
Moreover, I have filed Japanese Laid-open Publication No. 8-41508. In this patent specification, metal chips containing at least one kind of ingredients or such metal chips mixed with thermosetting resin or the like as raw material are pressed with heating while being electrified to produce a porous sintered plate. When the porous sintered plate thus obtained is used as a sound absorber, a sound insulator and a sound proof and anti-vibration material, the sound absorbing property, the sound insulation property, and the thermal insulation property can be enhanced. When the sintered plate is used as an electromagnetic shielding material, the conductivity can be enhanced. The molding apparatus disclosed in Japanese Laid-open Publication No. 8-41508 is the same as that of Japanese Patent No. 2,848,540, and also those shown in FIGS. 4 and 5 of U.S. Pat. No. 6,031,509.
The porous sintered plates produced as described in Japanese Patent Publication No. 58-5252and Japanese Laid-open Publication No. 8-41508 have excellent sound absorption and thermal insulation properties and a high conductivity as described above. However, the shapes of the obtained sintered plates are flat only. Furthermore, the sintered plates are slightly thicker in the centers thereof as compared with the peripheral portions thereof, and the surfaces of the sintered plates are slightly rugged. For this reason, to eliminate dispersions in thickness from the products, it is necessary to cut the surfaces of the sintered plates after the sintered plates are produced, so as to have a uniform thickness. That is, it is necessary to normalize the products. Moreover, if such a sintered plate is charged in a precision machine, it is also necessary to finish the surface of the sintered plate smoothly.
When the surfaces of the sintered plates are cut, the functions thereof such as the sound absorption and thermal insulation properties inherent in the sintered plates are deteriorated, caused by the reduction in thickness of the sintered plates. Moreover, voids exposed to the cut surfaces are different is shape and size, which causes dispersions in their performance as anti-vibration materials. That is, the normalization becomes unstable. Furthermore, the manufacturing costs of the sintered plates are remarkably increased, due to the additional cutting and finishing work.
Moreover, since the shapes of the sintered plates are flat only, uses of the sintered plates as anti-vibration materials and electromagnetic shielding materials have a limitation. Thus, the sintered plates are useless in effective anti-vibration or soundproof of apparatuses having an especial shape. That is, the sintered plates lack in general-purpose applicability. Even if such a flat plate-shaped sintered plate is cut to predetermined shapes and sizes, and the pieces are combined to be bonded, individually, so as to be applied in especial uses, the cost is so high that the practical application is impossible.
I have intensively investigated to solve the above-described problems of the porous sintered plates. As a result, it has been enabled to produce a high-functional porous structural material relatively easily.
Accordingly, it is an object of the present invention to provide a porous structural material having a solid shape with a curved surface, of which the general-purpose applicability is superior.
It is another object of the present invention to provide a porous structural material having a smooth surface and a high dimensional accuracy.
It is still another object of the present invention to provide a porous structural material having a high thermal insulation property and light in weight.
It is yet another object of the present invention to provide a process for forming a porous structural material comprising two steps, that is, molding and compacting.
It is still a further object of the present invention to provide a process for forming a structural material in which an intermediate molding product and a metallic sheet are metallurgically bonded, and simultaneously, the porous structural material is molded.
A porous structural material of the present invention is made from metallic chips containing at least one kind of ingredients. The structural material comprises a solid-shaped body having a smooth and curved surface, which is reformed by compacting a plate-shaped intermediate product in the hot state. The product is a molding with heating under a pressure while being highly electrified. In the structural material, pores on and near the surfaces are coarse and pores on the inside are dense in the direction of thickness.
A structural material of the present invention may be also composed of plural layers containing a metal sheet. The structural material comprises a body made from metallic chips containing at least one kind of ingredients and at least one metal sheet disposed on one or both sides thereof. The body is reformed by compacting an intermediate product and the metal sheet and bonded metallurgically to each other by heating while being electrified when compacting. The intermediate product is a molding with heating while being highly electrified. Preferably, in the structural material, the metal chips are shaved particles of aluminum-silicone alloy and the metal sheet is an aluminum sheet.
In a first forming process of the present invention, it is needed that metal chips containing at least one kind of ingredients are mixed, and charged into a molding frame at an approximately uniform level. An apparatus useful for forming is the same as the molding apparatus disclosed in Japanese Laid-open Publication No. 8-41508. The metal chips in the molding frame are compacted into a flat-plate shape with heating while being highly electrified. When the metal chips are mixed, glass particles, ferrite powder, cement powder and/or thermosetting resin in an amount of up to 25% by weight may be added. The metal chips are heated near the melting point when they are compacted. If the heating temperature is excessively low, the intermediate product is ready to be distorted. Thus, the dimensional accuracy of the finished product is deteriorated.
In the first forming process, the obtained intermediate product in the fevered state is removed, is set in a metal mold and compacted at a higher pressure than that applied in the reforming step. As a result, the intermediate product is reformed into a solid shape having a substantially uniform thickness and a curved surface. Then, the porous structural material as the finished product is removed from the metal mold. The intermediate product may be removed in the fevered state and cut to a required size and the respective cut pieces are charged in a mold to be compacted.
The temperature for compacting decreases from the heating temperature at compacting. However, preferably, the intermediate product is compacted in the hot state in which the internal temperature of the intermediate product is at least about 85 to 90% of the melting point of the metallic chips. For this reason, it is necessary immediately to set the intermediate product in a metal mold when the product in the fevered state is removed. If the internal temperature of the intermediate product is decreased to about 85% or less of the melting point of the metallic chips, it is difficult to reform the intermediate product into a solid shape of high dimensional accuracy.
Referring to a second forming process of the present invention, the metallic chips containing at least one kind of ingredients are mixed. An apparatus useful for the forming is the same as that disclosed in Japanese Laid-open Publication No. 8-41508. The metallic chips in a molding frame are compacted into a thin plate shape with heating under a pressure while being highly electrified. After cooling, at least one metal sheet is put on one or both sides of the intermediate product, set in a metal mold and reformed with heating under a pressure while being electrified by causing an electric current to flow across the upper and lower molds having a function as electrodes.
In the second forming process, the upper and lower molds may be a pair of rolls. The metal sheet put on one or both sides of the intermediate product is passed between a pair of the rolls to be re-pressed with heating while being electrified. Preferably, to obtain a solid shape, the metal sheet put on one or both sides of the intermediate product is re-pressed with heating while being electrified by causing an electric current to flow across the upper and lower molds.